Method and device for echo cancellation

Details Method and device for echo cancellation Method and device for echo cancellation

1999-11-04

2004-08-03

Barnie, Rexford (Department: 2643)

Telephonic communications

Echo cancellation or suppression

C379S406020, C379S406060, C379S388030, C379S387020, C379S390010

Reexamination Certificate

active

06771771

ABSTRACT:

This application claims priority to an application entitled “Echo Canceling Device and Method” filed in the Korean Industrial Property Office on Nov. 4, 1998 and assigned Ser. No. 98-47094, the contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to echo canceling, and in particular, to a device and method for preventing the degradation of echo canceling performance due to saturation.
2. Description of the Related Art
In general, a term “echo” refers to a phenomenon when the sound output from a speaker is fed back to a microphone and then is output again through the speaker or returns through a wire or wireless line. When this feedback occurs, it is difficult to restore the original sound. In most cases, the feedback is so great that it drowns out the original signal by generating a high-pitched tone.
Referring to
FIG. 1
, there is shown a block diagram of a prior art device for echo canceling. First and second amplifiers
100
and
1
amplify analog input signals, while analog-to-digital (A/D) converters
100
and
160
convert analog input signals to digital signals. In addition, digital-to-analog (D/A) converters
130
and
150
convert digital input signals to analog signals, while a digital signal processor (DSP)
140
performs echo canceling according to an echo canceling routine prepared therein in addition to general audio processing. An third amplifier
170
amplifies an input signal and provides the amplified signal to an input/output (I/O) connector
190
, and an fourth amplifier
180
amplifies a signal input from the input/output connector
190
. Finally, input/output connector
190
is connected to other internal or external audio processing blocks.
In an attempt to solve the echo problem of the prior art, the digital signal processor
140
performs convolutional coding for an audio signal input through a microphone and subtracts a specific value obtained by the coding from an audio signal output from a speaker. In this manner, the feedback is suppressed.
More specifically, an audio signal input through the microphone is input to the amplifier
100
designed to have a constant gain. The signal amplified by the amplifier
100
is then converted to a digital signal by the analog-to-digital converter
120
. The converted digital audio signal undergoes convolutional coding with a specific filtering coefficient in the digital signal processor
140
. A value obtained by convolutional coding is subtracted from a signal output to the speaker, thereby suppressing the echoes. However, in this echo canceling method, when the surrounding sounds of the external environment increase in level, the filtering coefficient and the input sounds exceed (or saturate) the processing limit of the digital signal processor. This results in the degradation of echo canceling performance.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a device and method for preventing the degradation of echo canceling performance due to saturation.
To achieve the above object, the present invention provides an echo canceling device comprising a first variable amplifier for variably amplifying an audio signal input through a microphone. The first variable amplifier responds to a control signal generated by a digital signal processor. The echo canceling device also comprises a first analog-to-digital converter for converting an analog signal output from the first variable amplifier to a digital signal. In addition, a second digital-to-analog converter is included for converting a digital signal output from the digital signal processor to an analog signal. There is similarly provided a second variable amplifier for variably amplifying a signal output from the second digital-to-analog converter, an input/output connector for connecting a signal output from the second variable amplifier to internal and external processing devices, and a sound measurer for measuring a level of surrounding sounds input through the microphone. The digital signal processor executes an echo canceling routine, performs general digital signal processing, and generates the control signals for controlling the first and second variable amplifiers according to the sound level measured by the sound measurer.


REFERENCES:
patent: 4984265 (1991-01-01), Connan et al.
patent: 4991166 (1991-02-01), Julstrom
patent: 5787165 (1998-07-01), Lilja et al.
patent: 5796818 (1998-08-01), McClennon et al.
patent: 6147979 (2000-11-01), Michel et al.
patent: 1169077 (1997-12-01), None
patent: 0400979 (1990-12-01), None
patent: 0515242 (1992-11-01), None
First Office Action dated Mar. 21, 2003 issued in a counterpart application, namely Appln. No. 99123512.6.

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